Rollup merge of #83388 - alamb:alamb/fmt-dcs, r=Mark-Simulacrum
Rollup merge of #83388 - alamb:alamb/fmt-dcs, r=Mark-Simulacrum

Make # pretty print format easier to discover

# Rationale:

I use (cargo cult?) three formats in rust:  `{}`, debug `{:?}`, and pretty-print debug `{:#?}`. I discovered `{:#?}` in some blog post or guide when I started working in Rust. While `#` is documented I think it is hard to discover. So taking the good advice of ```@carols10cents```  I am trying to improve the docs with a PR

As a reminder "pretty print" means that where `{:?}` will print something like
```
foo: { b1: 1, b2: 2}
```

`{:#?}` will prints something like
```
foo {
  b1: 1
  b2: 3
}
```

# Changes
Add an example to `fmt` to try and make it easier to discover `#`

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust